1. Field
Subject matter disclosed herein relates to a memory device, and more particularly to write performance of a phase change memory.
2. Information
Phase change memory (PCM) may operate based, at least in part, on behavior and properties of one or more particular phase change materials, such as chalcogenide alloy and/or germanium antimony telluride (GST), just to name a few examples. Crystalline and amorphous states of such materials may have different electrical resistivities, thus presenting a basis by which information may be stored. The amorphous, high resistance state may represent a stored first binary state and the crystalline, low resistance state may represent a stored second binary state. Of course, such a binary representation of stored information is merely an example: Phase change memory may also be used to store multiple memory states, represented by varying degrees of phase change material resistivity, for example.
In one example, a PCM memory cell may transition from an amorphous state to a crystalline state by applying a bias signal to the memory cell. Characteristics of a bias signal, such as peak magnitude and/or pulse width, for example, may be selected to allow a transition to a crystalline state. An improper selection of bias signal characteristics may result in a failure to transition to a crystalline state. Accordingly, such an improper selection may result in a PCM memory cell comprising a mixture of material in an amorphous and a crystalline state, which may lead to an undefined memory cell state resulting in a failure of the PCM memory cell, for example, or in decreased reliability (e.g., higher drift, lower data retention, and/or reduced endurance). On the other hand, a proper selection of bias signal characteristics may be relatively difficult to determine because biasing conditions for individual memory cells in a PCM may vary.
In another example, a reset pulse may be applied to a PCM memory cell to drive a phase transition from a crystalline state to an amorphous state. In one case, the amplitude of such a reset pulse may fail to result in a desirable size of an amorphous region of a PCM memory cell. Accordingly, such a PCM memory cell may lack an ability to retain data for relatively long periods of time at relatively high temperatures, such as for ten or twenty years at 85 C, for example. In another case, the amplitude of such a reset pulse applied to a PCM memory cell may be relatively large as to damage the PCM memory cell or to induce a memory cell failure during set and/or reset cycles, for example, after a relatively large number of such cycles, such as one million cycles, for example.